I have a 2000 Klein Quantum (this one, 2x9 speed: https://www.bicyclebluebook.com/value-guide/product/45657/) My shifters have been replaced once already with used 105 (also 5500), but now they have a lot of issues and I would slowly like to upgrade the whole groupset.
Can I start by switching out the shifters and derailers with new Sora R3000 parts (also 9 speed)? Or would I have issues with the brakes/crankset/etc? This would put me back on the road while I save for the rest. Thanks for any help, this is my first time here.